Metal coating process

ABSTRACT

A method for producing a permanently adherent image on an aluminum substrate is disclosed. The process comprises basically three areas of preparation; including (1) surface preparation of the aluminum substrate, (2) a screening procedure to apply the design or nomenclature to the aluminum substrate, and (3) a procedure for applying a protective lacquer to the screened image to permanently protect the screened image.

United States Patent 11 1 451 Nov. 20, 1973 Hahn METAL COATING PROCESS OTHER PUBLICATIONS [75] Inventor: w'lham Hahn Plymouth l-liett et al., Silk-Screen Process Production, Bland- [73] Assignee; Radium Corporation, ford Press Ltd., Third Ed. 1960, pp. 168, 169

Morristown, NJ. Primary ExaminerRalph S. Kendall [22] 1972 AttorneyDean S. Edmonds et a1.

[21] Appl. No.: 236,784

[57] ABSTRACT 52 US. Cl. 148/6.2, 117/38, 117/45, A method for Producing a Permanently adherent 7 5 117/132 BE image on an aluminum substrate is disclosed. The pro- 51 1m. 01. 1144a 1/52, c23r 7/26 cess comprises basically three areas of Preparation; 58 Field of Search 117/38, 45, 75, 132 BE; including Surface Preparation of the aluminum 143/62, 627 substrate, (2) a screening procedure to apply the design or nomenclature to the aluminum substrate, and 5 References Cited (3) a procedure for applying a protective lacquer to UNITED STATES PATENTS the screened image to permanently protect the d 2,471,909 5/1949 Spruance 148/62 screene Image 2,911,333 11/1959 Schuster et al. 148/62 3 Claims, N0 Drawings METAL COATING PROCESS BACKGROUND OF THE DISCLOSURE 1. Field of the Invention This invention relates to a method for applying an image such as a trademark design on a metal substrate and more particularly to an improved method for applying a design or nomenclature to an aluminum substrate and coating the substrate with a protective lacquer.

2. Description of Prior Art The art of applying a screened design or other image on a metal substrate has found numerous industrial applications. For example, in the automobile industry manufacturers have seen fit to display their seal or corporate name or trademark on a metal plate which is secured to the automobile. Although numerous processes have been used for applying such images on a metal surface, these methods have resulted in products which have exhibited numerous disadvantages. For example, these products which are used as exterior automobile hardware are subject to all extremes of weather conditions. In order to maintain a good appearance during the lifetime of the automobile it is necessary that the hardware exhibit excellent corrosion resistance without blistering or color change, and excellent adhesion of the image to the underlying metal surface. To date, however, it has generally been found that a good deal of the processes presently being used do not produce a product excelling in all of these desired characteristics.

It is therefore, the principal object of this invention to overcome the disadvantages of prior art processes by providing an improved method for producing a permanently adherent image on a metal substrate, in particular, an aluminum substrate.

SUMMARY OF THE INVENTION The present invention contemplates a relatively simple and efficient method for producing a permanently adherent image on a metal substrate, such as, for example an aluminum substrate, and thereby allows for increasing the life expectancy of structural parts having these images thereon when used, for example, as exterior automobile hardware.

The method for producing a permanently adherent image on an aluminum substrate in accordance with the present invention comprises mechanically buffing a surface of the substrate to a bright satin finish. The substrate is chemically cleaned by submerging the substrate in a warm non-etching aluminum cleaning solution for about four minutes, the solution being at a temperature of, say, about 125 to 175F. A chromate conversion coating is applied to the surface by (1). submerging the substrate in an acidic aqueous chromateion containing solution at room temperature for about thirty seconds, (2) rinsing the coated substrate in water, and (3) drying the coated substrate. A colored resinous enamel image in the form of a design or nomenclature is then applied to the coated surface by a screening process. The substrate is heat treated at a temperature ranging from 250F to 350F for a period of time from l5 minutes to an hour. A protective transparent epoxy coating is applied on the screened image by spraying the image with a transparent epoxy lacquer. The lacquer coated substrate is then heat treated 2 at a temperature of about 250F to 325F for about fifteen minutes to an hour.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To produce a permanently adherent image on an aluminum substrate in accordance with the invention requires three major steps as follows: (1) surface preparation of the aluminum substrate; (2) screening the design or nomenclature on the aluminum substrate; and (3) application of a protective lacquer.

In carrying out this procedure aluminum blanks, such as blanks of series 1,100 aluminum sheet, are first mechanically polished to a bright satin finish by polishing with a satin finish buffing wheel. Thereafter, these blanks are subjected to a chemical cleaning operation. Cleaning the samples involves the use of a non-etching aluminum cleaner such, for example, as a good detergent type or solvent type cleaner. After soaking the samples for a sufficient time, say several minutes at F, the blanks are removed from the cleaning solution and rinsed in water.

After cleaning the aluminum blanks it is necessary to chemically treat the buffed surface upon which the image will be placed to obtain proper adhesion of the screening inks and the protective lacquer coatings which are subsequently applied to the substrate. This surface preparation is best accomplished by forming on it a chromate conversion coating. To form such coating the aluminum blanks are placed in a bath containing an acidic aqueous solution (pH 1-3) containing chromate or dichromate ion at a concentration of l to 10 ounces per gallon, e.g., 7.5 oz. 1 gal., at room temperature, for say about thirty seconds. Thereafter the blanks are rinsed well in water and allowed to dry in air.

The screening procedure by which the desired design is applied involves screening transparent and/or opaque images onto the substrate using water soluble cut film or photo-screens having a 325 mesh stainless steel mesh backing. Opaque colors such as black synthetic gloss enamel and fire red synthetic gloss enamel may, for example, be applied to the chemically treated aluminum substrate along with a transparent blue color, by successive screening operations, to form a multi-color design on the blank. The opaque and transparent colors are baked to harden them. The baking operation typically requires one-half hour at 250F for the opaque colors and one-half four at 250F for the transparent colors, and each color is baked before the next is applied.

Once the screening operation is completed, the screened image on the aluminum substrate may receive the top coating or the protective lacquer application. Preferably, however, the screened substrates are allowed to stand for 24 hours before applying the protective lacquer coat. After this period of time, the second surfaces are sprayed with a clear epoxy lacquer coating. After spraying, the lacquer is allowed to flow out for approximately 2 minutes and thereafter is tackdried in an infrared (radiant lamp) oven. The lacquer coated substrates then are baked in a conventional type oven at a temperature of 250F to 325F for 15 minutes to an hour. The resulting lacquered product then is ready for embossimg, blanking, shearing, or any of numerous other mechanical operations that may be required to make the design finished emblem, label or other product.

Samples produced by following the process described above have been subjected to the various tests generally required by industry prior to acceptance. Some such tests and the results obtained with emblems made in accordance with the invention are as follows:

1. Sample emblems were inserted into a Singleton salt spray test unit and subjected to a Copper- Accelerated Acetic Acid Salt Spray (Cass Test) for periods of 6 and 22 hrs. These samples exhibited no blistering and substantially no corrosion.

2. Sample emblems were placed in a weathering apparatus which subjected the samples to extremes of three principal weathering agents, namely synthetic sunlight, moisture and temperature changes. After 500 hours in this apparatus the samples exhibited no appreciable change in color.

3. With a sharp knife, an X" was cut on the screened images of several emblems. An adhesive tape was placed over each of the X markers and firmly pressed on the samples to assure good contact between the tape and the screened surface. The tape was then pulled off rapidly. On all of the samples, 100 percent of the colored design remained firmly attached to the substrate.

4. Sample emblems were soaked in both a gasoline and SC-lOO solvent for fifteen minutes, removed from the bath and then wiped dry with a cloth. The coatings on the samples were found to be resistant to softening when wiped, exhibited no detectible swelling and returned to their original gloss and color.

5. Sample emblems were inserted into a Singleton Salt Spray Test unit and subjected to a Neutral Salt Spray Test percent concentration of Sodium Chloride for a period of 96 hrs. These samples exhibited no blistering and substantially no corrosion.

6. Sample emblems were tested in an Environmental Chamber Associated Testing Laboratories, Inc. Model ELHH-4-MR/LC. This instrument is utilized for humidity testing. The samples were exposed to 100F 100 percent Relative Humidity for a period of 96 hrs. These samples displayed no blistering, no corrosion and no creepage along the scribed line area of the test.

7. Samples were also placed under water at a temperature of F i lF for a period of 2 hours. Samples were taken out of the water immediately scribed with an X and tape tested with Scotch No. 710 tape. The samples exhibited 99 percent of the paint remaining in the tested area.

I claim:

1. A method for producing a permanently adherent image on an aluminum substrate comprising the steps of a. mechanically buffing a surface of the substrate to a bright satin finish;

b. chemically cleaning said substrate by submerging the substrate in a warm non-etching aluminum cleaning solution for about at least several minutes;

c. applying a chromate conversion coating to the surface by:

i. submerging the substrate in an acidic aqueous chromate-ion containing solution at room temperature for about 30 seconds;

ii. rinsing the coated substrate in water; and

iii. drying the coated substrate,

d. applying a colored resinous enamel image to the coated substrate by a screening process;

e. heat-treating the substrate at a temperature ranging from about 250F to 350F for a time from 15 minutes to an hour;

f. applying a protective transparent epoxy coating on the screened image by spraying the image with a transparent epoxy lacquer; and

g. heat-treating the lacquer coated substrate at a temperature of about 250F to 325F for from 15 minutes to an hour.

2. A method according to claim 1 wherein the lacquer coating is applied to the screened image about 24 hours after the heat treatment of step (d).

3. A method according to claim 1 wherein the substrate is subject to a rinsing operation in water after step (b). 

2. A method according to claim 1 wherein the lacquer coating is applied to the screened image about 24 hours after the heat treatment of step (d).
 3. A method according to claim 1 wherein the substrate is subject to a rinsing operation in water after step (b). 